1. Field of the Invention
The present invention relates to an endoscope provided with a first bending portion bendable in a plurality of directions and a second bending portion bendable in a plurality of directions in an insertion portion inserted into a subject to be examined.
2. Description of the Related Art
In recent years, endoscopes inserted into subjects to be examined have been widely used in medical and industrial fields. By inserting its elongated insertion portion into the subject, an endoscope can be used to observe a region to be examined of the subject and perform treatment or the like.
Here, a configuration is well known which is provided with, for example, a bending portion which is bendable in a plurality of directions at an insertion portion of an endoscope. The bending portion improves a progressive property of the insertion portion of a crooked part inside a duct. The bending portion also makes variable the observation direction of an observation optical system provided at a distal end portion located ahead (hereinafter simply referred to as “forward”) of the bending portion in a longitudinal direction in the insertion portion.
Since a plurality of bending pieces are connected together along the longitudinal direction of the insertion portion, the bending portion is normally configured to be freely bendable in four directions: up, down, left and right. More specifically, the bending portion can be freely bent in any one of the four directions: up, down, left and right, by pulling any one of the four bending operation wires (hereinafter, simply referred to as “wires”) from an operation section.
Note that the four wires are inserted into the insertion portion so as to be freely movable forward or backward in the longitudinal direction and a distal end of the wire in the longitudinal direction (hereinafter, simply referred to as “distal end”) is fixed to a bending piece located closest to the distal end side in the longitudinal direction (hereinafter, simply referred to as “distal end side”) among the plurality of bending pieces.
Note that the bending portion formed to have a shorter length in the longitudinal direction, that is, the bending portion with the smaller bending radius can turn in a small turning circle. This improves ease of passage of the distal end portion of the insertion portion with respect to the crooked part in the duct, causes the observation optical system provided at the distal end portion to easily approach the region to be examined, and is therefore advantageous.
This is because when the bending portion is formed so as to be long in the longitudinal direction, if a medical endoscope, for example, is inserted into the large intestine, the distal end portion strikes the crooked part of the large intestine, causing the field of view to be easily lost. That is, the shorter the bending portion, the less likely it is for the distal end portion to strike the intestinal wall at the crooked part. Note that, to reduce the length of the bending portion, it is only necessary to reduce the number of bending pieces connected.
However, when the bending portion is formed to be short, if the bending portion is bent, its distal end portion is caused to pass through the crooked part of the large intestine, the insertion portion is pushed in from a proximal end side in the longitudinal direction (hereinafter simply referred to as “proximal end side”) to make an attempt to move the distal end portion ahead of the crooked part, that is, to cause the bending part to pass through the crooked part, this results in the bending portion thrusting the intestinal wall—a so-called stick phenomenon. This makes it difficult for the bending portion to pass through, and as a consequence insertability of the insertion portion may deteriorate.
Furthermore, in the case of a medical endoscope, the following technique is generally used. After the distal end portion passes through the crooked part, the crooked part is straightened by pulling the proximal end side of the insertion portion with the distal end portion and the bending portion caught in a tissue in the body cavity first. Then, the insertion portion is pushed in from the proximal end side to allow the bending portion to pass through the crooked part.
FIG. 13 is a diagram schematically illustrating a state in which a second bending portion together with a first bending portion is bent rightward (RIGHT direction) on a distal end side of an insertion portion of a conventional endoscope and FIG. 14 is a cross-sectional view along a line XIV-XIV in FIG. 13 of a first bending portion and a second bending portion.
Japanese Patent Application Laid-Open Publication No. 7-116104 discloses a configuration as shown in FIG. 13 in which two bending portions 110 are provided as a first bending portion 101 and a second bending portion 102 on a distal end side of an insertion portion 106. Furthermore, Japanese Patent Application Laid-Open Publication No. 7-116104 discloses a configuration in which the first bending portion 101 is singly bendable and the second bending portion 102 is bendable together with the first bending portion 101, and it is thereby possible to keep constant the length of the bending portion 110 in a longitudinal direction S. In addition, Japanese Patent Application Laid-Open Publication No. 7-116104 also discloses a configuration in which only the first bending portion 101 is freely bendable, and it is thereby possible to reduce the bending radius.
More specifically, as shown in FIG. 13 and FIG. 14, Japanese Patent Application Laid-Open Publication No. 7-116104 discloses a configuration in which perimeters of four wires 111r, 111l, 111u and 111d (wires 111u and 111d are not shown) inserted in the insertion portion 106 are respectively covered with first coil sheaths (hereinafter referred to as “inside coil sheaths”) 112r, 112l, 112u and 112d (inside coil sheaths 112u and 112d are not shown).
Japanese Patent Application Laid-Open Publication No. 7-116104 also discloses a configuration in which a distal end of each inside coil sheath 112r to 112d is fixed to a connection pipe sleeve 115 that connects a first bending piece 101k located at a rearmost position (hereinafter simply referred to as “rear”) in the longitudinal direction S among a plurality of first bending pieces 101k making up the first bending portion 101 and a second bending piece 102k located at a frontmost position in the longitudinal direction S among a plurality of second bending pieces 102k making up the second bending portion 102. A configuration is further disclosed in which a proximal end of each inside coil sheath 112r to 112d is simultaneously switched between a fixed state and an unfixed state by a switching mechanism provided in the operation section.
Japanese Patent Application Laid-Open Publication No. 7-116104 further discloses a configuration in which perimeters of the respective inside coil sheaths 112r to 112d are covered with second coil sheaths (hereinafter simply referred to as “outside coil sheaths”) 113r, 113l, 113u and 113d (outside coil sheaths 113u and 113d are not shown). Japanese Patent Application Laid-Open Publication No. 7-116104 also discloses a configuration in which a distal end of each outside coil sheath 113r to 113d is fixed to a distal end of a flexible tubular part 105 and a proximal end of each outside coil sheath 113r to 113d is fixed to a proximal end side of the flexible tubular part.
On the other hand, while the fixing of the proximal end of each inside coil sheath 112r to 112d is canceled if, for example, the wire 111r is pulled using the bending operation mechanism provided in the operation section, the first bending portion 101 and the second bending portion 102 are bent toward the RIGHT side with the distal end of the outside coil sheath 113r as a starting point. On the other hand, while the proximal end of each inside coil sheath 112r to 112d is simultaneously fixed if, for example, the wire 111r is pulled, only the first bending portion 101 is bent toward the RIGHT side with the distal end of the inside coil sheath 112r as a starting point.
FIG. 15 is a cross-sectional view along a line XV-XV in FIG. 14 illustrating an example where inside the second bending piece making up the second bending portion, a left inside coil pipe that moves toward the RIGHT side in FIG. 14 is shifted toward the DOWN side and FIG. 16 is a cross-sectional view illustrating an example where the left inside coil pipe that moves toward the RIGHT side in FIG. 14 is shifted toward the UP side.
FIG. 17 is a partial cross-sectional view along a line XVII-XVII in FIG. 13 illustrating an example where the second bending portion is bent deviated from the RIGHT side to the DOWN side and FIG. 18 is a partial cross-sectional view illustrating an example where the second bending portion in FIG. 13 is bent deviated from the RIGHT side to the UP side.
Note that in FIG. 15 and FIG. 16, each wire 111r to 111d is omitted for simplicity of illustration.
Here, as shown in FIG. 15 and FIG. 16, various components are provided in the second bending piece 102k such as a signal cable 120 that extends from an image pickup unit provided in the distal end portion 103 of the insertion portion 106, a treatment instrument insertion duct 121 that is opened in a front end face 103s, a forward water feeding channel 122 and a light guide 123 that supplies illuminating light to the front end face 103s of the distal end portion 103. Since the positions of the various components in the second bending piece 102k are not fixed, the positions are always not constant.
Thus, the left inside coil sheath 112l that moves toward the RIGHT side as the second bending portion 102 is bent toward the RIGHT side comes into contact with each component in the second bending piece 102k as it moves. Accordingly, the left inside coil sheath 112l does not always move from the UP-DOWN direction toward the exactly 90° RIGHT side, but it may be shifted from the RIGHT side toward the DOWN side while moving toward the RIGHT side as shown in FIG. 15. In addition, the left inside coil sheath 112l may be shifted from the RIGHT side toward the UP side while moving toward the RIGHT side as shown in FIG. 16.
Note that in this case, the up inside coil sheath 112u and the down inside coil sheath 112d also slightly move toward the RIGHT side as shown in FIG. 15 and FIG. 16.
Thus, as shown in FIG. 15, if the left inside coil sheath 112l is shifted from the RIGHT side toward the DOWN side while moving toward the RIGHT side, the bending direction of the second bending portion 102 is also shifted from the RIGHT side toward the DOWN side as shown in FIG. 17. As a result, if the left inside coil sheath 112l is shifted from the RIGHT side toward the UP while moving toward the RIGHT side as shown in FIG. 16, the bending direction of the second bending portion 102 is also shifted from the RIGHT side toward the UP side as shown in FIG. 18.
FIG. 19 is an enlarged cross-sectional view of a wire guide section provided for the first bending piece shown in FIG. 14 and FIG. 20 is an enlarged cross-sectional view of the left inside coil pipe in FIG. 14.
Here, as shown in FIG. 14, a configuration is well known in which each wire 111r to 111d is inserted into the first bending piece 101k and a plurality of guides 130 which are tubular guide sections that hold each wire 111r to 111d to run along the inner surface of the first bending piece 101k. 
Thus, when the plurality of guides 130 shown in FIG. 14 are fixed to the second bending pieces 102k, each inside coil sheath 112r to 112d is inserted into each guide 130, and the guide 130 holds each inside coil sheath 112r to 112d to run along the inner surface of the second bending piece 102k, if the second bending portion 102 is bent, for example, toward the RIGHT side, it is supposed to be able to prevent each inside coil sheath 112l, 112u, 112d from moving toward the RIGHT side inside the second bending piece 102k. 
However, with a plurality of stranded wires being twisted, the wire 111r to 111d are configured to be rigid. For this reason, the wires 111r to 111d are never disordered in shape even when they come into contact with the inner surfaces 130n of the guides 130 and less likely to wear out. However, the inside coil sheaths 112r to 112d are configured to be flexible so as to be bendable together with the second bending portion 102 by winding an elemental wire 112s as shown in FIG. 20. Accordingly, when the left inside coil sheath 112l slides forward or backward in the longitudinal direction S through a through hole 130i of the guide 130 as the second bending portion 102 is bent toward the RIGHT direction, if the inside coil sheaths 112r to 112d come into contact with an inner surface 130n or a corner section 130c of a distal end 130s or a proximal end 130k as shown in FIG. 19, an array of the elemental wire 112s is disordered as shown in FIG. 20, and a so-called pitch shift a occurs.